1. Field of the Invention
The present invention relates to a barrier device provided in front of an image pickup optical system to protect an image pickup lens, and also relates to an image pickup apparatus having the barrier device.
2. Description of the Related Art
Generally an image pickup apparatus such as a digital camera is provided with a barrier mechanism in front of an image pickup lens barrel to protect an image pickup lens from dust invaded from the outside. This kind of barrier mechanism is disclosed in Japanese laid-open patent publication (Kokai) No. H7-159856 (JP H7-159856A), for example.
The barrier mechanism disclosed in the publication is provided with a pair of barrier blades, which can open and close an image pickup aperture of an image pickup optical system, in front of an image pickup lens barrel. The barrier blades are driven to open and close by a barrier drive ring that rotates around an optical axis. When closing the barrier blades, a rotation cylinder of the image pickup lens barrel is rotated in a clockwise direction. When a rotating force of the rotation cylinder is transmitted to the barrier drive ring via a connecting shaft, the barrier drive ring rotates in the clockwise direction while charging a barrier opening spring. At this time, the barrier drive ring pushes the barrier blades to rotate in a counterclockwise direction, which closes the barrier blades to cover the image pickup aperture in front of the image pickup optical system.
On the other hand, when opening the barrier blades, the rotation cylinder is rotated in the counterclockwise direction, which rotates the barrier drive ring in the counterclockwise direction. This releases a pressure to the barrier blades from the barrier drive ring, and the barrier blades rotate in the clockwise direction by a spring force of the charged barrier opening spring. This rotation opens the barrier blades, which opens the image pickup aperture in front of the image pickup optical system.
In recent years, a wide lens with a large effective optical path diameter is in increasing demand. The wide lens requires wide-area barrier blades in the barrier mechanism that uses the pair of barrier blades as shown in the above-mentioned publication. However, the larger the size of the barrier blades is, the larger the diameter of the image pickup lens barrel is in order to secure an escape space for the barrier blades when the barrier blades open.
Then, a method of increasing the number of the barrier blades is devised instead of enlarging the size of each barrier blade. For example, a barrier mechanism disclosed in Japanese laid-open patent publication (Kokai) No. 2007-102086 (JP2007-102086A) is provided with a first barrier blade group having three barrier blades that are rotatably supported by a pivot and a second barrier blade group that pairs off with the first barrier blade group and has three barrier blades similarly.
Each barrier blade group is provided with first and second springs, and one driving lever. The first spring gives a force in a direction to close the barrier blades and the second spring gives a force stronger than that of the first spring in a direction to open the barrier blades. The driving lever is driven by an external force to interrupt the spring force of the second spring to the barrier blades. When opening the barrier blades, the external force is not given to the driving lever. Accordingly, both the spring forces of the first and second springs are applied to the barrier blades. Since the spring force of the second spring is stronger than that of the first spring, the barrier blades open. When closing the barrier blades, the external force is given to the driving lever to interrupt the spring force of the second spring to the barrier blades. This closes the barrier blades by the spring force of the first spring.
However, since the barrier mechanism of the above-mentioned JP2007-102086A needs one driving lever and two springs for each barrier blade group, a component count increases, and the space therefor is also required.